Each MH manufacturer could wide them differently. On our 06 Winnebago E450, radio power comes from either Ford chassis or house batteries. Winnebago ran sides from the house system under the can floor carpet to a switch in the panel by the drivers left knee, they also modified the Ford wiring and then brought the two Ford not sides (radio memory and radio operating) to the switch. It is labelled Radio House Batteries or Ford chassis batteries). When camping it allows use of the radio without killing the chassis battery. It's possible that the power for the mirrors is also picked up in this area as well. I honestly don't know which system powers my mirrors. I
I also read that one RV manufacturer ran the sides from the house batteries to the dash area through the stepwell and had inline fuses under the plastic drivers step cover.
Ken